Physical Influences on Phytoplankton Ecology: Models and Observations

Sophie Clayton, Ph.D., 2013Mick Follows, Advisor

The physical environment in the oceans dictates not only how phytoplankton cells are dispersed and their populations intermingled, but also mediates the supply of nutrients to the surface mixed layer. I explore both of these aspects of the interaction between phytoplankton ecology and ocean physics. I have approached this topic in two distinct ways, working with a global ocean ecosystem model, and collecting data at sea.

I find that phytoplankton diversity, in a complex ecological model, can be enhanced through a combination of physical dispersal, environmental variability and nutrient supply. Diversity "hotspots" associated with western boundary currents and coastal upwelling zones are sustained through a combination of these factors.

A fine scale biogeochemical survey of the Kuroshio Front reveals patterns in physical, chemical and biological properties driven by both the large scale horizontal and smaller scale vertical physical dynamics of the region. A genomic analysis of the clade distributions of the picoeukaryote Ostreococcus strongly supports the model-derived hypotheses for hotspot formation. Strikingly, two distinct clades of Ostreococcus co-occur in most of the samples. A "hotspot" of Ostreococcus diversity appears to be supported by the confluence of Oyashio and Kuroshio water masses, enhanced frontal nutrient supply and regional mesoscale variability.